This disclosure relates in general to digital beamforming of antenna arrays, but not by way of limitation, to digital beamforming of antenna arrays utilizing distributed signal processing of time offsets amongst other things.
Antenna arrays offer a way of increasing the data rate and the signal to noise ratio of a signal. In addition, beamforming is a signal processing technique used in sensor arrays for providing directional signal transmission or reception of multiple array elements. Beamforming takes advantage of interference to change the directionality of the array. When transmitting, a beamformer controls the time, phase, and relative amplitude of the signal at each transmitter, in order to create a pattern of constructive and destructive interference. When receiving, information from different sensors is combined in such a way that the expected pattern of radiation is preferentially observed.
When a signal is coming from a direction that is not orthogonal to the plane of a planar antenna array, the signal arrives at the different array elements at different times. By adjusting the relative times that samples are taken from the received signal at the different array elements, the directionality of the receiving antennas can be electronically steered to match the direction of the incoming signal. This increases the signal to noise ratio and can enable higher data rates. Similar methods can be used to adjust the directionality of transmit signals.
Instead of adjusting the times of reception and transmission, phased arrays use waveforming techniques to adjust the relative phase offsets of the array elements during sampling of received signals or transmitting outgoing signals. The change in phase is analogous to a change in time, but only for a specific frequency. Different frequencies will vary in phase differently for a given time difference. This makes phased array techniques unsuitable for large bandwidth operations.
Regardless of which methods are used, the computational complexity of beamforming operations increases as the number of array elements in the array grows. This growth in complexity can be detrimental to characteristics of the overall system, characteristics including cost, size, weight, power consumption and heat produced by the system, for example. Often one or more of these characteristics limits the size of the antenna array systems that are practical. In addition, the scalability of systems can be difficult when a central processor performs the beamforming operations. For example, if an antenna array has 100 elements and a central processor performs the beamforming operations of all 100 elements, the central processor could require twice the computing power to support 200 elements. This linear growth of computing power of the central processor can be a major factor in limiting the scalability of antenna array systems. It is also difficult to route the signals from a large number of elements to a central processor.